1. Field of the Invention
The present invention relates to a compact zoom lens system and a digital camera using the compact zoom lens system, and more particularly to a compact zoom lens system and a digital camera using the compact zoom lens system having a wide half angle of view and a high resolution.
2. Discussion of the Background
In recent years, digital cameras or electronic cameras have rapidly come into widespread use in place of conventional cameras using a silver film. A typical digital camera shoots a subject with a solid image pickup device such as an image pickup device including a CCD (charge-coupled device), for example, and obtains image data including a still image and/or a motion image. The obtained image data is recorded in a digital fashion in a non-volatile memory or the like (e.g., a flash memory) provided to the digital camera.
The market of the digital cameras is huge and accordingly user needs for such digital cameras expand in a various directions. In particular, a high image quality and downsizing are constantly required and share a relatively large part of the user needs. Therefore, a zoom lens system used as an image pickup lens system is also needed to satisfy the needs for both performance enhancement and downsizing.
In an aspect of downsizing, a total lens length which is a distance from a plane of a lens closest to the subject to an image plane is needed to be reduced. Further, in an aspect of performance enhancement, a ultra fine resolution is required through an entire zoom range to cover at least three- to six-million elements of the image pickup device.
In addition, from a viewpoint in which many users demand that wide-angle lenses have wider angles of view, a half view angle at a short focal length edge in a zoom lens is preferably greater than 38 degrees. A half view angle of 38 degrees corresponds to a focal length of 28 mm in a 35-mm silver-film camera.
There are many kinds of zoom lens systems which may be available for the digital cameras. Amongst, one exemplary zoom lens system which is suitable for a compact digital camera system may include, arranged sequentially from a subject side, a first optical lens group having a negative focal length, a second optical lens group having a positive focal length, and a third optical lens group having a positive focal length. This zoom lens system further includes an aperture diaphragm which is mounted to the subject side of the second optical lens group in a manner such that the aperture diaphragm and the second optical lens group are integrally movable. Further, when the scaling Of the zoom lens system is changed, for example, from the short focal length edge to the long focal length edge, the second optical lens group monotonously moves from the image side to the subject side and, at the same time, the first optical lens group moves in such a way that a displacement of the image plane caused by the scaling change is corrected.
The above-described zoom lens system is described in some reference art documents including Japanese Laid-Open Patent Application Publication, No. 10-39214, No. 10-104518, and No. 2001-296476, for example.
However, even with these documents, a digital camera has not been introduced, having a compact size, a capability to obtain a sufficiently wider half angle of view over 38 degrees, and a reasonably fine resolution for a pickup device of a 3- to 6-million pixel range.